Generally, in a calciner in a cement manufacturing process, a pulverized coal is used as a fuel for heating and calcining a cement material in the calciner.
As is illustrated in FIG. 3, the cement manufacturing facility provided with this calciner includes: a rotary kiln 1 for burning a cement material; a preheater 3 provided with a plurality of cyclones 4a to 4d which are provided on a kiln inlet part 2 of this rotary kiln 1 in the left side of the figure; a chute 5 for feeding the cement material from the cyclone 4d in the lowermost stage of this preheater 3 to the kiln inlet part 2 of the rotary kiln 1; an exhaust line 9 having an exhaust fan 10 which is connected to the cyclone 4a in the uppermost stage and discharges a combustion exhaust gas; a main burner 7 for heating the inner part of the rotary kiln, which is provided at a kiln outlet part 6 in a right side in the figure; a clinker cooler 8 for cooling a cement clinker that has been burnt, which is provided at the kiln outlet part 6; and further a calciner 12 having the lower end to which the combustion exhaust gas is introduced from the kiln inlet part 2 of the rotary kiln 1 through a duct portion and also having a combustion device of the pulverized coal provided therein which is fed from a not-shown fuel feed line, between the cyclone 4c in the third stage and the cyclone 4d in the fourth stage. For information, there is also a cement manufacturing facility having the calciner 12 provided in another path which is different from the duct portion on the kiln inlet part 2.
In a cement-clinker manufacturing facility having the above described structure, the above described cement material which has been fed to the cyclone 4a in the uppermost stage shall be preheated by a high-temperature exhaust gas which is sent from the rotary kiln 1 and ascends from the lower part, as the cement material falls down sequentially to the cyclones 4 in the lower part, then be extracted from the cyclone 4c, be sent to the calciner 12, be calcined in the calciner 12, and then be introduced into the kiln inlet part 2 of the rotary kiln 1 from the cyclone 4d in the lowermost stage through the chute 5.
On the other hand, the combustion exhaust gas which has been discharged from the rotary kiln 1 shall be sent to the cyclone 4d in the lowermost stage through the calciner 12, be sequentially sent to the cyclones 4 in the upper part to preheat the above described cement material, and finally be exhausted by the exhaust fan 10 from the upper part of the cyclone 4a in the uppermost stage through the exhaust line 9.
By the way, in such a cement manufacturing facility, the concentration of nitrogen oxides (hereinafter referred to as NOx) in the exhaust gas to be discharged from the exhaust line 9 by the exhaust fan 10 is regulated by the Air Pollution Control Law. For this reason, the cement manufacturing facility monitors the NOx concentration in the combustion exhaust gas at all times and controls the NOx concentration in the exhaust gas so that the concentration does not exceed the above described regulation value, by removing the NOx by appropriately spraying ammonia water, sludge containing ammonia water or the like into the exhaust line 9, or by lowering the temperature in the rotary kiln 1 by adjusting the amount of fuel of the main burner 7, as are described in the following Patent Literatures 1 and 2, and the like.